A digital images that has been captured—using a variety of devices—can be stored on computer-readable storage media, rendered on a display device, and/or processed using an image processing computer software application. A digital image—which is formed from a collection of discrete picture elements, or “pixels”—can be stored on a computer-readable storage medium (for example, a hard disk of a computer system) essentially as a matrix of numbers. Each number represents a grayscale or a color scale value associated with a pixel, the collection of which collectively constitute the digital image. When the image is rendered on a display device, the numbers are passed through a lookup table (LUT) that maps the image intensity values to brightness values. If the LUT is linear, then the image can be mapped directly to the display. Otherwise, if the LUT is non-linear, the displayed image may not be an exact representation of the underlying image and thus must be further processed before being rendered on the display device.
In the context of color images, an appearance of the digital image on a display device can be manipulated by modifying the color values associated with the pixels that constitute the image. One technique to do so is referred to as “gamma correction” in which the color scale value of each pixel (typically normalized between 0 and 1) is exponentiated to a gamma value as shown in equation (1).Rprocessed=RF  (1)
In equation (1), R is a red component of an RGB color space value. Gamma correction according to equation (1) includes determining corresponding values for a green component (G) and a blue component (B).
For gamma, γ, values greater than 1.0, image processing according to the function referenced by equation (1) can increase a contrast of an image to make the image, when displayed, appear darker than its corresponding original image. Such image processing also can decrease highlight regions of the original image by darkening color scale values that constitute the highlight regions. Alternatively, image processing based on a gamma value of less than 1.0 can cause a decrease in a contrast by making the output image appear lighter overall relative to the original image. Consequently, processing in this manner can enhance the shadows of the original image.